#include <iostream>
#include <cmath>
#include <iomanip>
#include <cstring>

using namespace std;

class Point
{
private:
    double x, y;

public:
    Point(double x, double y) : x(x), y(y){};
    //友元函数
    double distance(Point p1, Point p2);
};
double Point::distance(Point p1, Point p2)
{
    return sqrt((p1.x - p2.x) * (p1.x - p2.x) + (p1.y - p2.y) * (p1.y - p2.y));
}

int main()
{
    int x, y;
    cin >> x >> y;
    Point p1(x, y);
    cin >> x >> y;
    Point p2(x, y);
    cout << fixed << setprecision(2) << p1.distance(p1, p2) << endl;
    return 0;
}

/*

*/